Thats what they made chlorine and filters for
Why we can't drink water directly from river or lake?
Oh you could, if you don't mind all the possible ill effects, like sickness and death.
Untreated surface water in rivers, streams, lakes, and ponds is not safe to drink unless it is treated to remove bacteria, viruses, and parasites.
Biological contaminants can come from sewers and failed septic systems, boat toilets, animals, and other sources.
At one time, you could .. At one time people would take their household drinking water from lakes and rivers and not even have to filter or treat it because there was no health risks .. Because at one time is was more pure and was not as contaminated as it seems to be now .. Now, due to human interference our sources of fresh water are becoming more and more contaminated with byproducts of one sort or another that have increased bacteria cultivation that it is no longer deemed "safe" to drink.
Who says you can’t…there are risks of course with any untreated water but depending on the proximity to population their may be no problem at all…the farther upstream of any population centers the better. With any contaminants it’s important to remember that the dosage is what is important. Don’t drink more than you need if you’re unsure about the purity. Our immune systems can handle a lot, though it is sometimes unpleasant. Your safest bet is treated water but don’t be afraid to drink from a stream in a survival situation. If it smells bad don’t touch it, if you can purify it with chlorine or UV light or other options, do it. That said, most of the water in rivers and lakes is going to dilute anything truly harmful to a point where it’s relatively safe to drink. I’d still look for the cleanest/coldest water I could find though. If you can find a spring that’s best, the water will be cold and clean coming from the spring.
River or lake water are not purified for drink So we don't drink water from river Or open place water. For safe purified water we have to use Water purifier.